[adventured]

The only explanation I've seen that makes any sense to me, is that their ad systems are still immature. They haven't figured out how to properly monetize their own platforms fully just yet, much less the rest of the Web.

Which also helps to explain why they get rated so poorly on return-on-investment when it comes to ad spending.

I'd say the last year has been a substantial break-through for Facebook in terms of pushing their ad systems forward and getting wide adoption of it (including finally getting mobile to spit dollars). Maybe a couple more years of developing their advertising platform and they'll get there.

I also think there's a general underestimation of how good the Google ad system is overall, and how hard it is to compete with.